Heat exchanger tubes with radially extending fins transversely connected thereto and method of forming the same



Feb. 6, 1962 w, DUMPLETON 3,020,027

HEAT EXCHANGER TUBES WITH RADIALLY EXTENDING FINS TRANSVERSELY CONNECTED THERETO AND METHOD OF FORMING THE SAME Filed Nov. 12, 1958 2 Sheets-Sheet 1 A is 3 INVENTOR. t Owen W. Dumplefon ATTORNEY Feb. 6, 1962 o. w. DUMPLETON 3,020,027 HEAT EXCHANGER TUBES WITH RADIALLY EXTENDING FINS TRANSVERSELY CONNECTED THERETO AND METHOD OF FORMING THE SAME Filed Nov. 12, 1958 2 Sheets-Sheet 2 INVENTOR. Owen W. Dumpleron ATTORNEY United States Patent m HEAT EXCHANGER TUBES WITH RADIALLY EX- TENDING FINS TRANSVERSELY CONNECTED glgfigETO AND METHOD OF FORMING THE Owen W. Dumpleton, London, England, assignor to Babcock & Wilcox LimitechLondon, England, a company of Great Britain Filed Nov. 12, 1958, Ser. No. 773,289 11 Claims. (Cl. 257-26216) This invention relates generally to tubular heat ex changers and more specifically to metallic heat exchange tubes having novel radial fins transversely connected thereto for augmenting the heat exchange surfaces and a method of forming the fins to the tubes.

For some heat exchange purposes it is possible to arrange for the heating medium to flow longitudinally over the heat exchange tubes, and in such an arrangement it is comparatively easy to secure longitudinally extending fins to the outside surfaces of the tubes to provide extended heat transfer surfaces.

In other heat exchangeapparatus it is necessary to operate with the heating medium flowing transversely over the heat exchanger tubes. The problem then arises that the fins must also extend transversely of the tubes, and one way of providing the fins is to weld them to the curved transverse surface of the tube.

In a large heat exchanger having transverse fins Welded to heat exchanger tubes to augment the heat exchange surfaces of the tubes, the welding of large numbers of fins to the tubes by the usual known methods, heretofore, was a relatively tedious, time consuming and expensive task.

An object of the present invention is to provide a relatively simple and inexpensive method of forming metallic heat exchanger tubes having transversely extending fins connected thereto. 7

Another object is to provide for anovel fin construction which can be readily connected transversely of the tube in an efficient, expedient and relatively inexpensive manner.

In accordance with this invention a metallic tube, suitable for use in a tubular'convection heat exchanger is provided on its outside with extended heat transfer surfaces inthe form of a multiplicity of longitudinally and radially spaced metallicmembers, each member comprising substantially parallel,v spaced plates arranged to extend outwardly and transversely of the tube axis, the plates being connected by a metal web portion which extends along at least part of theradially inner edge of the parallel plates; and each member being secured to the tube by resistance welding thewebportion thereto.

The invention also includes a tubular heat exchanger comprising at least one tube according to the preceding paragraph, arranged for the flow of cheating or cooling fluid over the plates in a direction transverse to the tube or in directions respectively transverse to the tubes.

3,020,021 Patented F eb. 6, 1962 the length of one tube of a tubulousconvection heat exchanger;

FIGURE 2 is a transverse sectional view through the tube taken on the line II-'II of FIGURE 1 and as viewed in the direction indicated by the arrows, and shows parts of welding members of a resistance welding machinesecuring fins to the tube; 9

FIGURE 3 is a longitudinal sectional view through the tube taken on the line III-III of FIGURE 2 and as viewed in the direction indicated by the arrows;

FIGURE 4 shows a modified form of the metallic member or fin.

FIGURE 5 shows a length of strip material prepared for bending for making another modified form of a metallic member or fin.

FIGURE 6 shows a length of strip material prepared for bending to form yet anothermodoified embodiment of a finor metallic member.

Referring first to FIGURES 1 to 3 of the drawings, a metallic tube length 1 of a tubular heat exchanger is located in a gas tight casing (not shown) through which heating gas flows in the direction indicated by the arrows 3, in-a direction which-is transverseto the axis 4 of the tube 1. The tube 1, for example, contains a fluid to be heated, the heat being transferred from the heating gas through the wall of the tube tothe fluid to be heated.

The quantity of heat transferred from the heating gas to the fiuid to be heated, which depends partly upon the area of metal available to absorb heat from the heating gas and the rate of heat transfer, is increased by the provision of extended heat transfer surfaces in the form of fins 5 provided on the outside of the tube 1.

According to this invention the fins 5 are each formed of a metallic member 7 comprising two parallel, spaced plates 9 arranged to extend outwardly andtransversely of the tube axis and connected together by a web 11 which, being of thesame width as the plates, extends along the radially inner edge of each plate 9 to join the two plates.

Thus each metallic member 7 is formed of a metallic strip material cut oil to predetermined length'and transversely bent in the region of its mid-length to bring the two end parts of the length side by side to constitute the two substantially parallel spaced plates 9. The central part of the metallic member at the bend forms the web 11. The strip material usedis generally rectangular in cross section having rounded edges which is apparent in FIGURE 1. Preferably the metallic strip or blank from which the fins are formed is substantially 1 inch wide and of an inch thick. The bend at the 1 mid-length is formed by bending the blank or strip about The invention furthermore includes a method of pro viding a metallic tube on its outside with extended heat transfer surfaces in the form of fins which extend transversely of the tube axis, including the steps of forming metallic members each comprising two substantially parallel, spaced plates extending side by side and joined by a web, presenting the members individually or in pairs to the tube, each with its web on the side of the metallic member adjacent the tube, and performing a resistance welding operation between the web and the tube.

The invention will now be described, by way of example, with reference to the accompanying drawings, in which:

FIGURE 1 is a side elevation of a segmental part of a former, preferably having a /s inch diameter, so that the two plates 9 are spacedapart uniformly at a distance of approximately /s of an inch.

The metallic members 7 are secured to the tube 1 in pairs, e.g. two at a time, as indicated in FIGURES 2 and 3, by means of an automatic resistance welding machine which'includes guides thathold the tube 1 centrally between two welding members 21, 31 disposed respectively at stations which are diametrically opposite with respect to the tube. The machine is adaptedto move the tube past these stations in a series of steps or movements, preferably a movement having a travel of 1 inch and after each of these movements the tube is held while the welding members 23, 31 bring two opposed members 7 into firm contact with the tube 1,whereupon the machine effects the resistance welding operation.

Welding member 21 includes a current carrying electrode 23 (see FIGURE 3) in the form of a copper blade 23A, 1 inch wide and /s inch thick having a rounded forward end 2313 and mounted in a holder 23C. ,The

length of the blade 23A is such that the end 233 thereof bears upon the web 11 of a metallic member 7, receiving the blade 23A, without the holder 23C contacting the outer end of the member 7. The welding member 21 also includes a two-jawed chuck 24, the jaws 24A, 24B of which are mechanically actuated to clamp the metallic member 7 in proper welding position in preparation for welding the same to the tube. The jaws 24A, 24B taper in width in a radially inward direction (see FIGURE 2). The second welding member 31 is similarly constructed to member 21 and includes a current carrying electrode 33 and a two-jawed chuck 34. Resistance welding machines having chucks for holding single fins for welding to tubes are well known and do not form part of the present invention.

The process of securing the metallic members 7 to the tube 1 is initiated by the feeding of metallic members '7 to each of the welding members 21, 31, whereby the member 7 is gripped by the respective chucks 24, 34 with the respective current carrying electrodes 23, 33 in place and bearing against the web 11. The chucks are swung s'idewardly away from the tube to facilitate insertion of the metallic members. The two welding members 21, 31 are then forced inwardly towards the tube to bring the two members 7 into forcible contact with the outer surface of the tube respectively at two diametrically opposite locations. A suitable welding current is then supplied, passing through one electrode 23, through the web 11 of the associated metallic member 7, through the wall of the tube 1, through the web 11 of the second metallic member 7, and thence to the electrode 33. The force to be applied by the welding members 21, 31, the magnitude and duration of the welding current and the permitted inward movement of the members 7 can readily be ascertained by experiment to produce the desired degree of fusion between the metallic members 7 and the tube 1. Preferably the resistance welding machine is completely automatic in operation, the chucks 24, 34 being automatically released and the electrodes 23, 33 automatically retracted at the end of the welding cycle. The tube 1 is then moved forward (to the left as viewed in FIGURE 3), again preferably automatically, a distance of 1 inch whereby the process of securing two metallic members 7 is repeated.

It will be seen that repetition of the operations described above will provide the tube with two diametrically opposite rows of metallic members 7. The tube 1 is then removed from the resistance welding machine, rotated through an angle of 30 degrees, and reinserted in the machine, but this time with an axial ofiset from its original position of /2 inch. On the welding machine being operated, two more diametrically opposite rows of metallic members 7 will be afiixed to the tube but displaced angularly about the tube by 30 degrees from the first two rows and with the metallic members 7 positioned axially along the tube midway between the members 7 aflixed to the machine during the first pass by the tube 1. After six passes through the welding machine, the tube 1 is provided with fins as shown in FIGURES l and 2.

The positions of the various metallic members 7 are shown clearly in FIGURES 1 and 2. There are twelve rows of metallic members added to the tube as six pairs of rows, paired as follows: rows 41A and 41B, rows 42A and 42B, rows 43A and 43B, rows 44A and 44B, rows 45A and 45B, and rows 46A and 46B.

The transverse center lines of the strips or blanks which form the members 7 of rows 41A, 41B; 43A, 43B; 45A and 45B lie in a first series of parallel planes which are transverse of the tube 1, and the transverse center lines of the members 7 in rows 42A, 42B; 44A, 4413; 46A and 46B lie in a second series of parallel planes which also extend transversely of the tube 1, but which alternate with and are evenly spaced betweenthe planes of the first series.

It will be seen that the members 7 are secured to the tube 1 in a plurality of circumferentially distributed, long1- tudinally extending rows in which the distance or space between plates 9 of each member being considerably less than the distance betwen adjacent members 7 in the same row, as it is readily apparent from a study of FIGURES 1 and 3. This spacing permits ready access for the chucks 24, 34 for holding the metallic members 7 during the welding operations, while still permitting the provision for a considerable amount of extended heat exchange surface in a compact fashion on the tube.

It will be seen from FIGURE 2 that, since the ciri cumferential surface of the tube 1 is curved and the webs 11 of the metallic members 7 are transversely flat, only the transversely, central part of each web 11, is actually fused to the tube metal. it follows that heat must flow inwardly from the side edges of the plates to pass through the central part of each web which is fused to the metal tube 1. It has been found that a considerable reduction of weight with a relatively small percent of reduction in heat absorption is obtained by the use of fins 5 having plate members 9 which are lenticular in cross section, i.e. plate members 9 having a relatively thick center part which tapers inwardly toward the edges thereof as shown in FIG. 4. As therein illustrated, a metallic member 7X is formed from a length of metallic strip or blank which is of lenticular cross section, cut to desired length and transversely bentin the region of its mid-length to bring the two end parts of the length side by side to constitute two substantially parallel spaced plates 9X, with the central part of the metallic member at the bend forming the web 11X. In the example shown in FIGURE 4, the strip or blank is preferably 1 inch wide and at its thickest, central region ,5 inch thick; the midlength bend being performed about a former of inch diameter. Consequently plates 9X are spaced apart of an inch in the central, radially extending region. Metallic members 7X, being of thinner metal and of smaller plate pitch A inch) than the plates 9 of members 7 inch) as in FIGURES l to 3, are mounted at a pitch 'of 0.8 inch along the tube. The chucks of the resistance welding machine are shaped to fit the leinticular shape of the plates 9X so as to avoid any rocking movement of the members 7X in the chucks during the welding operations and the ends of the electrodes are shaped to fit the web 11X to insure a large contact surface for the passage of welding current to the web.

It has been found that when the plates, which are lenticular in cross section have a transverse width: maximum thickness ratio of 4:1 or more, good heat transfer characteristics with low weight are obtained. These two dimensions are apparent in FIGURE 4 for the plates of lenticular form and denoted respectively by W and T.

A reduction in the weight of the metallic member and a reduction in the force needed to bend the member at its mid-length is obtained by cutting away part of the metal of the strip or blank before it is bent to bring the two end parts of the strip side by side to form the two plates.

Thus FIGURE 5 shows a length 50 of strip material or blank, the central region 50A of which is of uniform thickness and the two side regions 59B ofwhich are tapered towards the edges of the strip. At the mid-length of the length 50 the two sides of the length are notched as indicated at 51. The position of the bend made in the length of strip is indicated by the dotted line 52.

FIGURE 6 shows a length 60 of strip material the central region 60A of which is ofuniform thickness and the two side regions ddB of which are tapered towards the edges of the strip. At the mid-length of the length 60 the center of the strip is slotted as indicated at 61. The position of the bend made in the length of strip is indicated by the dotted line 62. In this form, the metallic member then has two spaced webs 63 connecting the end parts which eventually form the two parallel plates of the metallic member. Both webs 63 are welded to the tube, thus permitting the metallic member 60 to fit or more closely adapt itself to the transverse curvature of the tube.

When the metal of the metallic member is cut away I as shown in FIGURE or FIGURE 6, it is necessary for the electrodes of the welding machine to be similarly cut away to avoid a Weld forming between the electrode and the tube. If more than one web is used, for example as shown in FIGURE 6, care must be taken to insure that the weld is effective, there being a tendency if the slot at 61 is too large for only one of the webs to tabe part in the welding operation.

Although the two plates in each of the embodiments described above are truly parallel, it has been found in practice that there is sometimes a tendency for the two plates of the member to spring apart somewhat, upon cooling of the weld between the metallic member and the tube so that, two plates parallel before the welding operation are only substantially parallel after the welding operation, a divergence of the order of degrees having been encountered.

When a tube is provided with extended heat exchange surfaces in the manner described above, since each metallic member includes two transversely extending plates or fins, the number of welding operations required to add a given number of fins is only half that required in a conventional arrangement in which each plate or fin would be welded in place separately.

While the instant invention has been disclosed with reference to a particular embodiment thereof, it is to be appreciated that the inventionis not to be taken as limited to all of the details thereof as modifications and variations thereof maybe made without departing from the spirit or scope of the invention.

What is claimed is: I

1. A tube construction comprising a metallic tube, suitable for use in a tubulous convection heat exchanger and a plurality ofmetallic fins connected to the outer surface of said tube to provide for extended heat transfer surfaces, said fins each comprising at least two substantially parallel, spaced plates arranged to extend outwardly and transversely of the tube axis and a rectilinear web portion which extends along at least part of the radially inner edge of each plate to join said plates, said web being disposed tangent to said tube in a plane extending transversely of said tube, and said fins being secured to the tube at the point of contact with said web by a weld.

2. The invention as defined in claim 1, wherein the Web portion extends along substantially the whole length of the radially inner edge of each plate and thefin being secured to the tube by a resistance weld between the web and the tube.

3. The invention as defined in claim 1, wherein the two plates are spaced apart by a distance approximately equal to the thickness of the plates.

4. The invention as defined in claim 1, wherein the fins are secured to the tube in a plurality of circumferentially distributed, longitudinally extending rows and the distance between said plates of each fin is considerably less than the distance between. adjacent fins in the same row.

5. A tube construction comprising a metallic tube,

extends along at least part of the radially inner edge of,

each plate to join said plates, said fins being secured to the tube by a weld, and each plate is of lenticulartransverse cross-section with a width/maximum thickness ratio greater than 4:1. 2

6. The invention as defined in claim 5, wherein the two plates are spaced apart in a central, radially extending region by a distance approximately equal to the greatest thickness of the plates.

7. The invention as defined in claim 6, wherein the members are secured to the tube in a plurality of circumferentially distributed, longitudinally etxending rows and the distance between the two plates of each member in a central, radially extending region between the plates is considerably less than the distance between adjacent members in the same row.

8. The invention as defined in claim 5 wherein said fin is provided with a notched web portion.

9. The invention as defined in claim 8 wherein the said web portion is notched inwardly from its marginal edge portions.

10. The invention as defined in claim 8 wherein said web portion is notched intermediate its edge portions.

11. 'A method of forming a finned tube for use in heat exchangers over which afiuid flows transversely with re-' spect to the longitudinal axis of the tube comprising the steps of forming a plurality of separate and distinct metallic fins by bending metal blanks so that each of the formed fins comprise a pair of substantially parallel spaced plates extending in side-by-side relationship joined by a rectilinear web portion, presenting a plurality of said formed fins to a tube so that the plates of said fins are disposed in planes extending transversely to the longitudinal axis of the tube with the web portion engaging the tube at a tangent point, simultaneously welding the presented fins to said tube at their tangent points so that all of the requisite welding current passes from one metallic fin to the tube and from the tube to the other metallic fin, and progressively advancing the tube after the welding step for receiving another plurality of fins to be welded thereto in a row with the preceding welded fins, and said tube being advanced a linear amount so that the distance between adjacent fins in the same row is greater than the distance between the pair of plates of each fin.

References Cited in the file of this patent UNITED STATES PATENTS 1,382,220 Murray June 21, 1921 1,689,568 Wade Oct. 30, 1928 7 1,764,603 Bell June 17, 1930 2,003,320 Trainer et al. June 4, 1935 2,261,136 Brown Nov. 4, 1941 2,473,633 Brown June 21, 1949 2,482,951 Vonk Sept. 27, 1949 2,965,744 Busse Dec. 20, 1960 

